In the telecommunications industry, and particularly the telephone industry, it is constantly necessary in order to enable hook-ups to be made, to access the conductors of protectively sheathed conductor cables, most commonly, polylethylene sheathed conductor cables. To accomplish this task, a tough protective polyethylene sheath and an underlying aluminum sheath must be cut and removed from a specific length of the cable without damaging the conductor elements which lie directly underneath the protective layers. This is a delicate task because, typically, the conductor elements are separated from the polyethylene and aluminum sheathing by only a relatively thin layer of paper or mylar, which provides negligible protection. As a result, there is a strong need for a cutter that is capable of cutting the polyethylene and aluminum sheathing both longitudinally and circumferentially to a precise depth without damaging the underlying conductor elements.
Because of the curved nature of the sheathing being cut, there is a tendency for any cutting blade to veer off the intended line of the cut, unless the cutting blade is supported laterally (across the line of cut).
Because considerable force is required to draw a blade through the tough protective sheathing layers, any occasion when the blade slips out of the sheathing being cut is necessarily followed by a somewhat violent "follow-through". This action endangers anything that lies in the path of the tool, including the operator's "non-cutting" hand. The tool of this invention overcomes this hazard by way of a blade which retracts immediately and forcefully upon disengagement with the material being cut by the tool. Cutting sheathing from conductor cable traditionally has been performed by the use of a fixed blade. But the lack of precision and the safety hazard presented by the use of a fixed blade has made such use prohibitive. Frequent injuries have resulted when the blade inadvertently slips out of the sheath during the cutting process. Cuts to the operator's non-knife holding hand which is usually used to hold the cable in place during the longitudinal cut, is a common occurence.
Precision in depth of cut has also been a problem due to the lack of any means for precisely determining the depth of cut when a fixed blade is used. The result is that conductor damage often occurs.
There is nothing in the prior art, to the inventors knowledge, that encompasses both a tool which is capable of precisely determining the depth of cut and has a safe, retracting blade in a form which is compact and streamlined and which is useful in confined quarters, where conductor cable sheathing is often being cut.
The inventor is aware of the following patents which disclose various forms of cutting tools:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 1,739,972 Klinger December, 1929 2,187,215 Spinello January, 1940 2,616,172 Parker November, 1952 3,906,561 Bawa September, 1975 3,906,627 Manning September, 1975 4,139,939 Crooks February, 1979 4,433,484 Antisdel et al. February, 1984 4,507,867 Haas, Jr. April, 1985 ______________________________________
Bawa does not disclose any means of precisely determining the depth of cut. Also, since his tool is attached to pliers as specified, it is too cumbersome for cutting sheathing from conductor cable. The blade in Bawa's device can easily be held in an extended position while cutting Bawa does not disclose any means of lateral support to maintain the line of cut.
Manning also does not disclose any lateral support means to maintain line of cut. In Manning's design the angle of blade cutting edge to the hand angle of the tool is inappropriate for the job of cutting sheathing on a conductor cable. Manning's blade can be held extended manually while cutting.
Haas, Jr. discloses a large cumbersome cable sheath cutter knife which is always exposed. His cutter knife design has no lateral support to maintain the line of cut and no depth control facility. Consequently the blade can easily cut or damage the underlying conducting elements of the transmission cable.
Antisdel discloses a desiqn of cutting knife. Antisdel has a projection which must pass between the conductors and the sheath thus increasing the force necessary to accomplish the task at hand. The thickness of the head must pass through the cut directly after the blade, which inhibits cutting action.
Crooks discloses a cutting knife desiqn but the angle of the cutting blade edge to the hand angle is awkward and inefficient. His design has no depth of cut regulation capability. He also does not provide any lateral support to maintain line of cut on a cylindrical object such as a conductor cable.
Parker discloses a slitter for cable coverings. The slitter has a depth control facility but the blade is not retractable. The cutter is large and cumbersome.
Spinello discloses an electrical insulation cutter which has a non-retractable blade that pivots about a pin which is positioned midway along the handle of the cutter. His cutter is inappropriate for cutting the sheath of large diameter conductor cables.
Lastly, Klinger discloses a cable splitter which has an exterior blade. The blade is not retractable. Moreover, there is no depth control facility in the Klinger cable splitter design.